Method of manufacturing alkyl carbonates



foct. 19 1926.

H. G. MITCHELL METHOD 0F MANUFACTURING ALKYL CARBONATES original FiledJuly 14, 1924 NW (mm.

tubaunaou ous arts.

Patented Oct.A 19, 1926.

vUNITEDsrzxrlas MARRY GILBERT MITCHELL, OF BALTIMORE, MARYLAND, ASSIGNORT0 U. S. INDUS- PATENT orifice.l

TRIAL ALCOHOL co., A CORPORATION or WEST VIRGINIA.

METHOD or MANUFACTURING ALKYI. .'cARBoNATEs.

Original application led .Tuly 14, 1924,

My invention relates particularly to a process for the manufacture ofalkyl carbonates but especially ethyl chlorocarbonate and diethylcarbonate, which will render the manufacture of the same commercrallypracticable so that the said products will be.

available for and capable of use in the vari- It is to be understood,however, that my process is applicable particularly to the production ofalkyl carbonates which are in the` same aliphatic series wlth diethylcarbonate.

The object of my invention is to provide a process for the production ofalkyl carbonates, and particularly ethyl chlorocarbonate -and diethylcarbonate, by means ofv which there will be a high yield,'while at thesame time the by products are recovered 1n an effective manner, thuspreventing damage which would result'from the-escape of the same. e -l 4Inasmuchasthis is a division of my application upon manufacture of alkylcarbonates, Serial No. 725,835, filed July 14, 1924, the object of myinvention is Ato carry out the manufacture of these products as setforth therein.

A further object is to conduct the process with the aid of phosgene gasformed from carbon monoxide and chlorine, in such a manner that thephosgene gas reacts with the alcohol at low temperatures so -as tominimize side reactions and losses resulting therefrom. Another robjectis to bring about the separation of the diethyl carbonate from the othermaterials contained in the resulting reaction mixture in an advantageousmanner so as to obtain high yields by avoiding distillation withconsequent hydrolysis and the formation of constant boiling mix tures'as lfar as possible.

A,v further object of my invention will appear from the detaileddescription of the same hereinafter. f

The three main reactions which take place in carrying out my process-are the following: y y

CO +Cl2+ COCl2 l f Y C0012 CQ'HSOH-CzI-LCOOCIH- HC1 02111500001|'C2H5OH-(C2H5)2CO3 -l- HC1y My invention is capable of being carried Serial No.l725,835. Divided and thisapplieation led March 25, 1925. SeriaLNo.18,350.

tion of an apparatus for use in connection with my invention.

In carrying out my lnvention may pro,

vide any suitable source of carbon monoxide to be supplied by a tube 1to a storage chamber 2 and thence by a tube 3 to a mixing tube 4.`However, for this purpose I 'prefer producergas which would, forexample, contain 25 to 40% of carbon'monoxide, 60 to 65% of nitrogen andsmall amounts of carbon dioxide, o gen and hydrogen. Chlorine 0btainedrom any suitable source of supply is fed by a'tube 5 to a storagechamber 6 and thence by a tube 7 to the mixing tube 4. The gases fromthe tubes 3 and 7 are supplied .at such; a rate as to mix the chlorineand carbon monoxide in the proportions of mol for mol of the/twogases.'l In `order to obtain v complete utilizationof the chlorine anexcess of the carbonmonoxide amountingto 25% above the theoreticalamount, is pre- H ferred. They are thence passed through a chamber 8'filled with activated charcoal or bone-black or provided with someother aption is exothermic the chamber 8 is cooled by means of a waterjacket 9. The temperature' in the `chamber 8 may be observed by means ofa thermometer 10, the temperature being kept below 250 C. in order toyavoid undesirable decomposition of the phosgene, although it is to beunderstood that in the first stage of the reaction, that is to say, thefirst contact between the gases, the temperature may exceed 250 C. ifdesired without detriment, but that preferably the nal tem- Vso ypropriate catalyst. Inasmuch as the reacperature of the gases uponleaving the cataf lytic chamber will not exceed `.110" C. The gaseswhich leave the catalytic chamber 8, and comprising phosgene, inertgases and an excess-.of carbon monoxide, pass out by a t tube-"11ste thelower end of a scrubber 12 filled with glass beads which is suppliedwith a descending current of. absolute alco` hol from a tank 13connected to the topof "the scrubber 12 by atube 14. l The-amount ofalcohol fed into the apparatus is preferably somewhat in excess of twomols of alcohol to one mol of phosgene. Inasmuch as the reaction in thelscrubber 12 between the alcohol and the phosgene gas and which resultsAthe escape of any alcohol or hydrochloric acid from the top of thescrubber, a small scrubber 16 supplied with a current of water is'provided at the top of the scrubber 12 Land connected thereto by meansof a tube 17. A tube 18 at the top of the sbrubber 16 permi-ts anyresidual gases to pass out of the -apparatus. The ethyl chlorocarbonateflows through a trapped tube 19 from the lower part of they scrubber 12to a series of flasks 20, 21, 22 and 23, having baflles 23a and@connected by overflow pipes 24, 25 and 26, while the flask 23 isprovided with a final overflow outlet pipe 27 for the diethyl carbonate.The first flask 20 is preferably not heated as sufficient heat isprovided by the contents of the flask but the other flasks 21, 22 and 23are heated by burners 28, 29 and 30 of any :desired character. Theheating Yof the contents of these flasks is carried out preferably in aperiod of from 4 to 5 hours and until the temperature reaches" 82 to 850C., which is the final boiling point of the mixture, the temperaturebeing observed by means of thermometers 31, 32, 33 and 34 contained inthese flasks. Any vapors formed in the flasks land which would containalcohol and vhydrochloric acid, are conveyed by a tube v25, connected tothe top of the flasks 21, 22

and `r23, to a reflux condenser 36 having a' water cooling jacket 37 andthe large amount` of hydrochloric acid present is finally collected in ascrubber 38 connected .by a tube 39 to the top of the condenser 36` thescrublber being filled'with glass beads and supplied with a current ofwater 39 for the absorption of the hydrochloric acid which passes outfrom the lower end of the scrubber through a trapped pipe 40 and theresidual gases escape from the top of the scrubbe)- by means of a tube41.

The diethyl carbonate coming from the vtube 27 is then treated in such away as to remove the impurities therefrom.- This is preferably done byadding to the solution containing diethyl carbonate flowing from thetube 27, a neutralizing agent, such, for example, as a solution ofcaustic potash in water, but preferably a 30% strength caustic sodasolution in water, the water being added in this way in suchl quantityas to make the solution neutral or slightly alkaline, andcontainingsuflicient water todissolve any precipitated sodium chloride.Preferably to lcounteract'the heat of-neutralization and to avoidhydrolysis of the diethyl carbonate due to increased temperatures, themixture is cooled tofrom 10 to 30o C. during the neutralization andisagitated. The mixture is then allowed toseparate into two layers, anupper ester layer containing approximatel 80% diethyl carbonate and 20%alcoho, with slight impurities, and a lower layer which is comprisedalmost entirely of a sodium chloride solution in water. The upper layermay then be decanted and, if desired, separated into its constituents byrectification. f I

The above process may be modified somewhat, if desired, by changing thesame to the extent of introducing with the phosgene an amount of thealcohol equal to 100% in excess of the amount theoretically required toform the diethyl carbonate. This procedure is, in fact, preferredinasmuch as when such an excess of alcoholis present the conversion ofthe ethyl chlorocarbonate to diethyl carbonate proceeds at roomtemperatures and is completed in about 48 hours without requiring theapplication of heat at this stage of the process, and as' whenconducting the process in this manner most of the hydrochloric acid isretained in the liquid.

Furthermore, in the purification of the final product, whether or notthe 100% excess of alcohol has been introduced, the diethyl carbonatemay be separated from the materials dissolved therein without previousneutralization, if desired, by the addition of water which will cause aseparation of the liquid into two layers. For this purpose generally anamount of water is added equal to from 3 to 5 times the volume of thediethyl carbonate solution, the amount of water, however, depending uponthe concentration of the ester solution and being addedV in an amountsufficient to reduce the concentration of the alcohol solution formed tosuch a point that the ester will be most effectively carried into theupper layer and the hydrochloric acid completely retained by the lowerlayer. That is to say, the alcohol obtained from the ester andalcoholsolution will be reduced in this way to a 10% solution of alcohol andwater inpthe lower layer when sufficient water has been added.

Again, if desired, instead the ester and alcohol solution coming fromthe tube 27 may be purified with the aid of inert solvents includingaromatic hydrocarbon solvents. such, for example, as benzol, toluol orxylol and aliphatic ethers such as ethyl ether, propyl ether. ethylmethyl ether, etc.

- rable from the ester,

When sufficient of the inert solvent has been added to completelydissolve the diethyl carbonate, Water is then added in sufficientquantity to make a complete separation of the constituents into twolayers. It will be understood, furthermore, thatthe quantity of theinert solvent which is used v'vill be such as to change the distributionlof the ester in the mixture as to cause a\separa' acid be insoluble inthe solvent and that the soLventbe inexpensive and ieadilyrecovervtoapproximately cal quantity required to form a, dialkyl car. -bonate andallowing n mately 100% Water thereto in a quantity able, although it isto be understood that the -solvents to be used these characteristics."

I'While I' have described my invention above in detail I Wish it to beunderstood that many changes may be made therein Without departing fromthe spirit of' vthe same.

1 claim 1. The process the^vapors of phosgcne into contact `with analiphatic alcohol in an excess' amounting `100% above the theoretithereaction mixture to stand luntil a dialkyl carbonate is formed,

2. The process which'comprisesbringing the vapors of phosgene intocontact with a'l/coholv in an excess amounting to approxiabove thetheoretical quantity 'required to formdiethyl carbonate and allowing thereaction mixture to stand'uiitil diethyl carbonate is formed. l

3. The process which comprises forming a dialkyl carbonate in a reactionmixture containing an aliphatic alcohol and phosgene in the absence ofan acid binding agent, adding an inert solvent for the dialkylcarbonate-Which in the presence of Water acts as la non-solvent for thealcohol layer formedto the vreaction suiiicient to form separate liquidlayers and removing the layaction mixture,

er containing kyl carbonate. y

4. The process Whi h comprises 4forming diethyl carbonate ina reactionmixture containing alcohol fand phosgene in the absence of an acidbinding. agent, adding an inert solvent for the diethyl carbonate-#whichin the presence of water acts as a non-solvent for the alcohol llayerformed-to y the renoed not have all.

-as a non-solvent which comprises bringingV mixture, adding l the largerpercentage of dialaddingwater thereto in' a"diethyl"carbona`te quantitysufficient to form separate liquid layers and removing the layercontaining the larger percentage of diethylcarbonate.V

5. The-process w ich comprises forming a dialkyl carbonate in a)reaction mixture containing an aliphatic alcohol and phosgene in theabsence off an' acid bindin'g f agent, adding benzol as an inert solventto the 'reaction mixture, adding water thereto in a quantity sufficient.to form separate liquid layers and removing the la er containing th'elarger percentage of dial'kyl carbonate. f

6. The process whichcomprises forming diethyl carbonate in a reaction4mixture con- .taining alcohol-.and pliosgene inthe absence of an acidbinding agent, adding benzol as an inert solvent to Vthe reactionmiture, adding water 'thereto in a quantity sufficient to form separateliquid layers and removing the layer containing the larger percentage ofdiethyl carbonate. l

7. The process which comprises forming.

ay dialkyl carbonate in a reaction mixture containing an aliphaticalcohol and phosgene in the` absence of an acid bindin agent, adding aninert solvent for the dial l carbonate-Which inthe presence. of wateracts forv theI alcohol layer formed-to the reaction. mixture, addingwater thereto in a quantity suilicient to form separate liquid layers,removing the layer containing the larger carbonate and distilling thelayer containing thel larger percentage of the ester formed to separatethe solvent therefrom.

l8. The process which 'comprises forming diethylicarbonate in a reactionmixture `.containing alcohol and phosgene in the absence of an acidbinding agent, adding an inert solvent-for the diethyl carbonate-Whichin the presence of Water acts as a non-solvent for the alcohol laverformedto there-action mixture, adding",water thereto in a quantitysufficient to form separate liquid layers, removing the layer containingthe larger percentage of diethyl carbonate and distilling the layercontaining the larger percentage of the ester formed to separate thesolvent therefrom. f

9. The process which comprises forming a dialkyl carbonatel in areactionmixture containing lan aliphatic alcohol and phosgene in theabsence of an acid binding agent, adding benzol as an inert solvent tothe reaction mixture, addingfvvater thereto in a quantity sufficient toform separate liquid layers, removing the ,layer containing the largerpercentage of dialkyl` carbonate'and distilling the layer containing thelarger percentage of the ester formed to separate the solvent therefrom.

- 10. The process which comprises forming in a 4reaction mixtureconpercentage of diallgyl l taining alcohol and phosgene in the absenceofA an acid binding agent, adding benzol as an inert solvent to thereaction mixture', adding Water thereto in `a quantity suicientto formseparate liquid layers, removingl the layer containing the largerpercentage-of diethyl carbonate and distilling the layer containing thelarger percentage of the ester formed to separate the solvent therefrom.

In testimony that I claim the foregoing, I have hereuntdsct my hand this20th day of March, 1925.

i HARRY GILBERT MITCHELL.

